While that is true you also have to consider the extra performance gain from a newer CPU which will Be equivalent in going from zen to zen 3 today and then there is the money I'll get back from selling my current CPU/ram/MB so the net spend won't be that much more.
I'm waiting to see the prices of new kit, especially mobos, before making a conclusion. I can see mid-range mobos pushing > £300 (for comparison, my x570 Tomahawk was £170... just wish I had a CPU to put in it )